1. Field of the Invention
The present invention relates to a power supply shunt regulator that includes a branch which, in turn, includes a series connection of at least a shunt switch and an inductive means and which is coupled in parallel with both a load and a power supply, said regulator including current limitation means for generating an analog control signal that is applied to a control electrode of said shunt switch so as to limit the amount of current flowing through said shunt switch.
2. Background
Such a power supply shunt regulator is already known in the art, e.g. from the article "Design and Development of a Sequential Switching Shunt Regulator", by I. R. White, Proc. of the 3d ESTEC Spacecraft Power Conditioning Seminar, Noordwijk (NL), 21-23 Sep. 1977, pp. 133-136, the entire contents of which is incorporated herein by reference. This prior art regulator is used to control the power supplied to the load by the power supply which comprises solar cells.
A problem with the prior art shunt regulator is that, when the shunt switch is turned on, the parasitic capacitance across a power supply discharges abruptly due to a short circuit which is established. The current peak caused by this discharge may damage the shunt switch and thus reduces the system reliability. This is all the more worrying when the frequency with which the shunt switch is turned on and off is relatively high and when the regulator is used in a spacecraft which requires very high reliability.
The known prior art regulator shown in FIG. 7 of the above-mentioned White article, limits this discharge current via a current limitation means which includes in particular a capacitor C1 shown in FIG. 4 of the White article. This capacitor artificially increases the Miller capacitance of the shunt switch, formed by transistors T2 and T3 shown therein, and thereby slows down the response of the regulator to limit the current flow through the switch to a value which is dependent on the parasitic capacitance across the power supply and limits the power supplied by the power supply.
Since the power supplied and the value of the parasitic capacitance are non-linear and are time and temperature dependent, this known regulator has to limit the current to a value which is substantially lower than a maximum current that may be required by a specific application, by taking into account the above variations. In this way, less current is available for the discharge of the parasitic capacitance which provides a slower discharge and consequently also provides a larger power dissipation time in the shunt switch. This larger power dissipation time diminishes the reliability of the regulator.
Moreover, the design of the prior art regulator such as disclosed in the White Article has to be redone for every application which is characterized by other parameters, for instance a different parasitic capacitance. A further drawback of this known regulator is that the shunt switch is made with bipolar transistors which, has a relatively high saturation voltage when turned "ON". Bipolar transistors dissipate relatively larger amounts of energy, thus complicating the design and increasing the dimensions of the regulator.